A gas turbine engine, such as an aircraft gas turbine engine, may in principle include an engine core with an axial-flow compressor, fuel injectors, combustors, an axial-flow turbine, and a rearwardly facing combustion-gas outlet. There may be many stages of compressors and many stages of turbines. When the gas turbine engine is in operation, air is drawn into the engine and compressed by the compressor, and fuel is added to the compressed air by the fuel injectors. The mixture of fuel and compressed air is ignited in the combustors. The resulting hot gas combustion flows through the turbine, whose turning drives the compressor, and out of the rear of the engine through the combustion-gas outlet. More complex versions of the gas turbine engine use a large-diameter turbofan driven by the engine core to increase the mass flow of air through a fan duct. This simplified description of the principles of the gas turbine engine omits the myriad of detailed features of the engine structure.
Cooling air may be required at various compartments and locations of the engine core, such as for the high-pressure turbine active clearance control and the low-pressure turbine active clearance control and for engine compartment cooling, and for general cooling. The cooling air may be provided by bleeding air from the fan duct and delivering it to the required locations through ducts affixed to the engine core. Desirably, the cooling air is delivered to the required locations through duct structures that have weights that minimized to the extent possible and in which the cooling air is not heated any more than necessary.
The engine core may in principle be covered with pairs of nacelle cowls that are arranged in a clamshell fashion over the generally cylindrical engine core. The nacelle cowls may be removed, usually by pivoting the cowls on hinges, to provide access to the engine core for maintenance. When the nacelle cowl is removed, the mechanic is faced with a complex array of structures, pipes, and ducts. The most readily accessible components often inhibit access to those that are further from the surface of the exposed engine core.
There is a need for an alternative engine structure in which weight is reduced, engine performance is improved, and access to the engine core is improved.